The growth of the post-volcanic carbonate platform and the depositional shallowing of basins.
After the magmatic activity ending, subsidence was often reduced in the western Dolomites, Val d’Adige and Brenta areas, whereas it remained active in the eastern portion of the Dolomites, were speeds of about 200 m/Myr were recorded. The post-volcanic platform therefore prograded in still-stand condition in some western areas, with moderate aggradation in the majority of the Dolomites. The basins were now often fed by large amount of volcaniclastic sediments and therefore basin floor depositionally aggraded, forcing the platform base of slope to migrate in a climbing way. The whole of the post-volcanic platforms is affected by a pervasive late diagenetic dolomitisation, significantly limiting the facies analysis potential. Some primary features are however visible within the dolomitised platform bodies (e.g. Sella Platform) and very well preserved facies are found in platform-derived olistoliths (so called Cipit Boulder, buried within argillaceous basinal units. Margin and slope facies remained similar to the synvolcanic ones.
Slope clinostratifications were less steep (25-35°) than in the pre-volcanic platforms, showing concave geometry in their lower portions. Base of slope units were well supplied in bio-intraclastic calcarenites. Resediment loose calcarenitic and micritic sediments were now able to reach the adjacent basins (Bänderkalke, upper Mb of the Buchenstein Fm; and Acquatona, Fernazza and S. Cassiano Fms), which also record the reappearing of ooid grains, that were absent in the region since the Lower Triassic. Terrestrial plant debris also reappears in these basinal deposits, witnessing moist climatic conditions and a northward shift of the terrigenous shoreline. In many areas, the post-volcanic platforms can be subdivided into two bodies (Cassian 1 and 2) by the recognition of a sharp discordance surface. The lowermiddle portions of the slope palaeosurface were onlapped by basinal terrigenous beds, almost completely deprived of platform derived carbonates and enriched in continental plant debris, suggesting a period of almost total interruption of the carbonate platforms growth. The two platform generations shear many sedimentary facies similarity. The younger portions are however often enriched in stromatoporoidsand coral fragments. The massive progradation of these platforms, associated with the strong aggradational evolution of the well sediment fed basins progressively filled the inherited accommodation space, while subsidence was slowing down. During the post-volcanic evolution, the Adige Valley area was almost deprived of subsidence and mainly stayed under subaerial conditions, developing deep karst structures.The middle Carnian sediment record a major change in the carbonate facies architecture, associated with the demise of the high relief rimmed platforms and theaccumulation of shallow-water loose terrigenous-carbonate sediments, witnessing the last Eastern Dolomites marine areas (Heiligkreuz Fm). These shallow water sediments colonised the form basin centre areas, while the previous carbonate platform emerged, witnessing a downward shift of the relative sea-level. The formation base is matched with a level of organic enrich claystones, with fresh water influences and strongly impoverished faunae. The following on the contrary record the growth of carbonate biostromes, with much diversified palaeontological associations, witnessing the appearing of the first “modern” colonial corals. No large reefs were however able to develop, and the unit grades upwards into peritidal dolomites, in turn capped by terrigenous-carbonate arenites, followed by a last carbonate unit. The arenitic unit is particularly noteworthy for its bearing some of the oldest known and better preserved ambers, preserving an extraordinary number of previously unknown micro-organism. This formation also bear important tetrapod foot-prints. The complete filling-up of any accommodation space correspond to a sharp emersion discordance. Tectonic reactivation was however soon matched with a renewed subsidence in the Dolomites, associated with the uplifting of metamorphic and Permian intrusive units in southern areas.
Sedimentation was dominated by reddish continental and marginal marine clays, sandstones, conglomerates, sulphate evaporites and some dolomite beds (Travenanzes Fm, previously known as Raibl Fm). Sedimentation restarted also in the Adige and Brenta area, grading into peritidal dolomites that were to characterise a large portion of the Norian and Rhaetian, in the Brenta and Dolomites areas.